Lamp terminal structure and method of manufacture



w. LEDIG El AL 2,216,247 LAMP TERMINAL STRUCTURE AND METHOD OFMANUFACTURE Oct. 1. 1940.

Filed m 28, 940

Fig. 2.

Inventor Willg Ledig}. Georg Trebbin, Heinz Seffer'i IIJ bww;

Patented Oct. 1, 1940 LAMP TERDIINAL STRUCTURE AND METHOD OF MANUFACTUREWilly Ledig, Berlin-Lichtenrade, Georg Trebbin,

Berlin-Spandau,

and Heinz Seflert,

Berlin,

Germany, assignors to General Electric Company, a corporation of NewYork Application May 28, 1940, Serial No. 337,730 In Germany April 5,1939 6 Claims.

Our invention relates to a seal and base construction for electricincandescent lamps and discharge devices particularly of the tubulartype, such as the commercially known lumiline and fluorescent lamps.More particularly, our invention relates to a method and apparatus forsealing and basing lamps of the above type.

The most usual method for sealing the customary stem tube to theenvelope of electric incandescent lamps and discharge devices consistsin sliding the envelope, which is provided with along neck portion, overthe glass lamp. mount and in subjecting that area of the necksurrounding the edge of the stem tube flange to scaling fires or flames.As a result, the heated portion of the neck softens and contracts untilit comes in contact with the stem tube flange and fuses therewith, thesuperfluous part of the neck separating and dropping ofii. It has alsobeen proposed to press the envelope neck slightly, near the sealingpoint, by means of special squeezing clamps or jaws in order that thelamp base which is' secured to the envelope neck, or the cement which isused for fastening the base, may secure a good hold behind the recessesproduced by such squeezing jaws.- Methods have also been employed inwhich the lamp envelope is out exactly to its final length before thesealing of the same, the sealed joint being subjected to the pressingaction of squeezing jaws so that the part of the envelope neck which initself is superfluous and constitutes only waste material can bedispensed with.

The method according to the invention likewise employs a lamp envelopeout exactly to its final length. However, the envelope and lamp mountare mounted on a metal ring member whose outer edge is bent or curledupwardly or inwardly towards the lamp envelope preferably in.

a curve somewhat in excess of a 90 are so that when the edges of theenvelope neck and the stem tube flange become softened through fusion,the glass will flow into and fill the annular recess formed by the saidcurled edge. Consequently, when the seal cools, the metal ring membershrinks slightly and in this manner presses with considerable forceagainst the glass bead within its rounded edge; The metal ring member isthus securely fastened to the end of the lamp envelope. A base is thenmechanically fastened to said metal ring member in definite relationthereto. In this manner the overall length of elongated tubular lampsand discharge devices can be easily and accurately controlled.

One object of our invention is to provide a seal and base constructionfor electric incandescent lamps and discharge devices.

Another object of our invention is to provide a method of sealing andbasing elongated tubular lamps and discharge devices of the double-endedI type whereby the overall length thereof may be easily controlled andmaintained within accurate limits.

Still another object of our invention is to provide apparatus forsealing the envelopes of electric incandescent lamps and dischargedevices.

Further objects and advantages ofuur invention will appear from thefollowing description of a species thereof and from the accompanyingdrawing in which:

Fig. 1 is a longitudinal cross-section of the apparatus employed to forma seal according to the invention, the lamp parts being shown mountedtogether in position preparatory to the sealing process; Fig. 2 is a topview of the heating element employed in the apparatus according to theinvention; Fig. 3 is a longitudinal sectional view of the finished sealcomprising our invention; Fig.

4 is a longitudinal sectional view of the end portion of a lamp providedwith the seal and base construction comprising our invention; and Fig. 5

is a top view of the metal ring member employed in the formation of thesealaccording to the invention.

, Referring to the drawing, the apparatus there shown comprises aheat-resisting block or base member i of insulating material, having acentral hole 2. Mounted on the block l is a heating element or band 3 ofsuitable heat-resisting metal which can be heated directly by means ofan electric current flowing therethrough. This heating band is likewiseformed with a central opening 2! which is aligned with the hole 2 in thebase member. A hollow stop pin 4 of heatresisting insulating materialextends up through the aligned openings 2 and 2i and is formed at itsupper end with-a conical head 5. A heat accumulator ring 6 of insulatingmaterial, having an enlarged opening 6', is concentrically mounted onthe heating band 3, this ring having the function of storing up heatduring the sealing process.

, The heating and fusion ofthe glass lamp partsto thereby form the sealis effected by the conduction of heat thereto from a metal ring member Iwhich is concentrically placed on top the heating band 3, within theopening 6' in the heat accumulator ring 6. This metal ring member I isitselfheated by conduction of heat from the heating band 3, the latterbeing heated bythe passage of current therethrough. To produce an 1even, uniform heating of the metal ring member I, the heating band 3must carry, on the surface on which the metal ring member I rests, thesame current density throughout. To obtain this result, the heating band3, because of the presence of the central bore 2| therein, is providedwith a number of small holes 22 and cuts 23, as shown in Fig. 2, whichare so arranged as to produce substantially equal current densities onthe surface on which the metal ring member I rests, i. e. they producean even distribution of the current density around the central bore 2|.

The metal ring member I may consist of any material which cansufliciently withstand the high temperature to which it is heated duringthe lamp sealing operation. It may consist, in particular, of a metalwhose coeflicient of thermal expansion is higher than that of the glassof which the lamp parts to be sealed are made. For instance, it mayconsist of copper. It is also possible to use a metal, for instanceiron, which will not adhere to the softened glass, since the metal ringmember I need not form a hermetically tight seal with the glass. Thehermetic seal is accomplished solely between the two glass parts to besealed together. The metal ring member I is provided at its outerperiphery with a curved flange 8 formed by bending or curling back theouter edge in a curve of at least 90 to thereby form an annular recesstherewithin. The ring member is further provided with a plurality ofinwardly extending bendable prongs 9 which may be partly formed bycutting back into the ring member proper.

In forming the seal according to the invention, the metal ring member Iis placed over the head of pin 4 and is concentrically mounted on theheating element 3 with its curled or bent edge 8 extending upwardly sothat the said member lies flat against the heating element. A lampmount, comprising a glass stem I I having a conventional conical flangeor flare III, is mounted in an upright position on the metal ring memberI so that the outer edge of the flange I0 rests on the said member. Theglass stem I I is provided with a pair of leading-in wires I2, I2 whichare sealed into the pressed portion of the glassstem and support afilamentary cathode I3 at their inner ends. The stem II is also providedwith an exhaust tube I l through which the envelope may be evacuatedand, if desired, filled with gas. To accommodate the exhaust tube I4 andleadingin wires I2, I2, the stop pin 4 is provided with a longitudinalbore I5 into which the exhaust tube and leading-in wires are insertedwhen the lamp mount is first placed on the metal ring member 7. Thediameter of the outer edge of the flare Ill corresponds approximatelyto, but is made slightly smaller than, the bent or curled flange 3 onthe ring member I so that the flare I 0 can pass within the curledflange I0 and rest on the flat portion of the ring member. With themetal ring member I and the glass stem I I in place, the open end of alamp envelope is then placed over the glass stem II. In the exampleshown, the lamp envelope I6 is of tubular shape and is provided with aneck portion I! of reduced diameter. The outer diameter of the neck I!is made approximately the same as the diameter of the outer edge of theflare I0 so that the neck I! can just rest on the edge of the flare.

To bring about the fusion of the glass envelope I6 and the glass stem II, a high current is passed through the heating element 3 so that thelatter, and the metal ring member I which lies thereon,

attain a temperature exceeding the softening temperature of the glass.The heat is then transmitted, by conduction and radiation, from the ringmember I to the glass parts I0 and I! so that the interengaging edges ofthe latter will soften and fuse together, the soft glass at the sametime flowing into the annular recess formed by the bent or curled flange8. During this sealing operation, a slight downward pressure may beexerted on the lamp envelope I6, In certain types of electricalincandescent lamps and discharge devices, such as the double-endedtubular type, it is necessary to maintain certain longitudinaldimensions. This can be very easily accomplished in our improved sealingmethod since the downward pressure exerted on the envelope I6 can be solimited by a suitable stop that the envelope, after the fusion, willhave just the desired length. The conical surface 5 on the head of pin Iis designed to provide a suitable seating surface or stop against whichthe flare II] can rest to thereby limit the downward movement of theglass stem I I during the fusion process. below the required limit.

When the glass envelope I6 and stem II are fused together completely soas to form a hermetic seal having an annular bead 25 fitting into thecurled flange B of the metal ring member I, the current flowing throughthe heating band or element 3 is discontinued, preferably by slowlyreducing the current in order that the stresses in the glass maygradually disappear by virtue of a sufficiently slow cooling process. Atthis juncture, the lamp envelope I6, with 'its finished seal, may beremoved from the sealing apparatus. The metal ring member I is securelyheld to the end of the lamp envelope by reason of the grippingengagement of the curled edge or flange 8 of said member with theannular bead of glass 25 formed at the end of the lamp envelope. Thesecure fastening of the metal ring member I to the glass bead 25 resultsfrom the shrinking of such member upon cooling; the member being ofmetal, it shrinks more than the glass. reason, it is not necessary touse. as the material for the ring member, a metal that has substantiallythe same coefficient of thermal expansion as the glass of the lampenvelope and stem, or a metal which will wet easily to the softenedglass. As a result, ordinary iron may be used for the ring member Iproviding the fusion point of such iron is higher than the softeningtemperature of the glass.

The metal ring member I not only facilitates the fusion between the lampenvelope I6 and stem I I and the maintaining of accurate lamp lengths,but because of its accurate and solid aflixation to the lamp envelope,it advantageously lends itself to the mechanical fastening of the lampbase to the lamp envelope, 1. e., without the use of cement. To thisend, the prongs 9 on the metal ring member I are bent outward at rightangles to the plane of said member, as shown in Fig. 3, so as to extendparallel to the longitudinal axis of the lamp envelope. A base I8,provided with openings I9 corresponding to the outwardly bent prongs 9and through which the latter may pass, is then placed over the end ofthe lamp envelope with the prongs extending into the openings I9. Thebase may be located in definite longitudinal relation with respect tothe ring member I by means of stop lugs or shoulders 26 formed on theinner side of the base, the lugs being adapted to engage the flatsurface of the metal ring mem- Consequently, the glass stem will notdrop For this I provided with bases at both ends.

ber l. With the base in this position, the outer ends of the prongs 9are then bent over the outer side of the base to thereby secure the baseto the lamp envelope. The openings I 9 are preferably enlarged at theirouter ends, as shown at 21 in Fig. 4, so as to accommodate therein theouter bent portions of the prongs 9 and so conceal them I within thebody of the base. Inasmuch as the ring member '1 serves to limit thelongitudinal dimension of the lamp envelope l6 during the sealingoperation, the accurate positioning of the base it is consequentlyassured. This feature is particularly important in the case of tubularlamps having bases on both ends. The base l8, which may consist, forinstance, of suitable insulating material, is provided with two or moremetal pins 2!], extending longitudinally of the lamp, to which theleading-in wires l2, l2 are soldered or otherwise connected. These pinsserve as the lamp terminals for conducting the electric current to thecathode l3, and also as means for mounting the lamp in its holders orsockets. However, the base could be provided, instead, with a lateralextension 24 likewise made of insulating material and carrying the lampcontacts or terminals. Such an arrangement permits a particularly shortbase design, thus minimizing the overall length of the lamp.

If desired, the metal ring member I may be connected to one of theleading-in wires l2 so that it may serve as one of the contacts of thebase, for-instance, as an external shell for the base. Furthermore, ametal disc may be used instead of the metal ring member I. In eithercase, however, a method of mounting the base is provided which permitsan accurate and very solid fastening of the same to the lamp envelopewith* out the use of the conventional basing cement.

It is evident that the improved method of seal ing and basing lampsaccording to the invention makes it easily possible to maintain thelongitudinal dimensions of lamp envelopes within accurate limits, anadvantage which is of especial importance in the case of tubular lampswhich are An accurate manufacture is possible because of the fact that acertain definite longitudinal pressure is exerted on the lamp envelopeduring the fusion process, so that the softened glass mass is formed orgathered up on the metal ring member in such quantities that the entirelength of the lamp envelope is reduced to a certain value. As a resultof the secure fastening of the metal ring member to the end of the lampenvelope, which takes place during the sealing process, the lamp basecan be applied very accurately since it may be fastened to the metalring member without the use of cement, the accuracy being higher in suchcase than in the case of the conventional methodof fastening wherecement is used.

What we claimas new and desire to secure by Letters Patent of the UnitedStates is:

1. An electrical device comprising a glass envelope havinga glass sternhermetically sealed to an end thereof, said envelope being provided withan outwardly extending annular bead immediately adjacent the said end ofsaid envelope, a metal ring member fitting over the end of said envelopeand having its outer edge upturned'over said annular bead and secureddirectly thereto, said ring member being provided with a plurality ofprongs, and a base fitting over the said end of said envelope andsecured thereto by said prongs.

2. An electrical device comprising a glass envelope having a glass stemhermetically sealed to an end thereof, said envelope being provided withan outwardly extending annular bead immediately adjacent the said end ofsaid envelope, a metal ring member fitting over the end of said envelopeand having a curled flange upturned over said annular bead and secureddirectly thereto, said ring member being provided with a plurality ofprongs, and a base fitting over the, said end of said envelope andsecured thereto by said prongs, said base having a plurality of openingsthrough which said prongs extend, the outer portions of said prongsbeing bent over said base to thereby secure said base to said ringmember.

3. An electrical device comprising a glass envelope having a glass stemhermetically sealed to an end thereof, said envelope being provided withan outwardly extending annular bead immediately adjacent the said end ofsaid envelope, a metal ring member fitting over the end of said envelopeand having its outer edge upturned over said annular bead and secureddirectly thereto, said ring member being provided with a plurality ofprongs, and a base fitting over the saidend of said envelope and securedthereto by said prongs, said base having an abutment shoulder forengagement with said ring member to thereby position said base indefinite relation with respect to said ring member in a directionlongitudinally of said envelope, said base having a plurality ofopenings through which said prongs extend, the outer portions of saidprongs being bent over said base to thereby hold said abutment shoulderagainst said ring member and secure said base to said ring member.

4. A method of sealing a lamp mount, comprising a glass stem tube havinga flare portion,

.to a glass envelope, which consists in placing said lamp mount in anupright position on a metal ring member the outer edge of which iscurled upwardly to form an annular recess adjacent the outer edge ofsaid flare, said ring member be-,

ing made of a metal having a higher fusion point than the softeningtemperature of the glass of which said envelope and lamp mount are made,placing the open end of said envelope over said lamp mount intocontiguous relation to the outer edge of said flare, and heating saidmetal ring member until the glass of said envelope and lamp mountsoftens and fuses together and flowsinto the annular recess formed bythe said curled edge of said ring member.

5. A method of sealing a lamp mount, comprising a glass stem tube havinga flare portion, to a glass envelope, which consists in placing saidlamp mount in an upright position on a metal ring member the outer edgeof which is curled upwardly to form an annular recess adjacent the outeredge of said flare, said ring member being made of a metal having ahigher fusion point than the softening temperature of the glass of whichsaid envelope and lamp mount are made, placing the open end of saidenvelope over said lamp mount into contiguous relation to the outer edgeof said flare, and simultaneously heating said metal ring member andapplying downward pressure to said envelope until the glass of saidenvelope and lamp mount softens and fuses together and flows into theannular recess formed and lamp mount are made, a ring member having itsouter edge curled through an arc in excess of ninety degrees and ofslightly greater diameter than the outer edge of said flare to thereby'ireceive said flare therewithin, placing said lamp mount in an uprightconcentric position on said ring member with the said flare disposedwithin the said curled edge of said ring member, placing an open end ofsaid envelope concentrically over said lamp mount into contiguousrelation to the outer edge of said flare, and heating said ring memberuntil the glass at the end of said envelope and the outer edge of saidflare softens and fuses together and flows into the annular recessformed 6 by the said curled edge of said ring member.

WILLY LEDIG. GEORG TREBBIN. HEINZ SEFFERT.

